The present invention relates generally to release devices, and more particularly, to a redundant fuse wire release device and redundant fuse apparatus that may be used to stow or release items such as solar arrays, antenna positioning mechanisms, reflectors, and the like, found on satellites, space stations, and spacecraft, for example.
Conventional prior art non-explosive release apparatus, such as a separation spool device, for example, is used to stow or release a captured member that constrains deployment of a spacecraft element, for example, such as a solar array, in a stowed position. In such apparatus, a single fuse wire acts as a locking member that fastens a tensioned member wrapped in tension around a split spool. When the tensioned member is under tension, the split spool is clamped to a portion of the device to be deployed (the captured member) which prevents deployment of the captured member, such as a solar array. Once the release device is actuated, the fuse wire unlocks by self-destructing, thereby releasing the tensioned member to unclamp the captured member and allow deployment.
However, such a single fuse wire locking member is subject to self-unlocking resulting from mechanical failure. The single locking member (fuse wire) can fail due to mechanical stress and cause premature release of the device. An electrical failure can also prevent the device from releasing if inadequate current flows to melt the fuse wire upon actuation.
To overcome the limitations of this conventional single fuse wire locking member, a redundant fuse for use with in a split spool device was developed by the assignee of the present invention is disclosed in U.S. Pat. No. 6,133,818, issued to Hseih, et al., and is an example of a redundant fuse wire design for an application similar to that of the present invention.
The redundant fuse wire design disclosed in U.S. Pat. No. 6,133,818 uses three individual fuses configured in a triangular shape preventing a round disk from release. It requires cutting two of three fuses to release the disk, and it prevents premature release if one fuse is accidentally cut, thus, it is single point fault tolerant.
The shortcoming of this redundant fuse wire design is that third fuse does not always get cut upon actuation, and thus it could potentially cause release hang up.
Also, with three fuses rigidly connected to three contacts, depending upon the accuracy of fuse wrapping tension, the load may not be equally shared by all there fuses, therefore it is possible for one or two fuses to be overloaded while the other is not loaded at all, resulting in a potential for fuse overload
In view of the above, it would be desirable to have a improved redundant fuse wire release device and redundant fuse apparatus.